# 新大小杜
# 在读研究生
# 开发时间，2021/5/1 17:08
class Instrument():
    def make_sound(self):
        pass
class Erhu(Instrument):
    def make_sound(self):
        print('二胡在演奏')
class Pinao(Instrument):
    print('钢琴在演奏')

class Violin(Instrument):
    def make_sound(self):
        print('小提琴在演奏')

def play(instrument):
    instrument.make_sound()

class Bird():
    def make_sound(self):
        print('小鸟在唱歌')
if __name__ == '__main__':
    play(Erhu())
    play(Pinao())
    play(Violin())
    play(Bird())